docs: def log_scalar(self, step, tag, val):
          '''
          Write a scalar event.
  
          :param int step: Time step (x-axis in TensorBoard graphs)
          :param str tag: Label for this value
          :param float val: Scalar to graph at this time step (y-axis)
          '''
          summary = Summary(value=[Summary.Value(tag=tag, simple_value=float(np.float32(val)))])
          self._add_event(step, summary)